Weighbeam control system



Dec. 6, 1966 AIR SUPPLY J. SORTEBERG WEIGHBEAM CONTROL SYSTEM Filed April '7, 1965 INVENTOR.

'-4 f ATTORNEY United States Patent C 3,289,933 WEIGHBEAM CONTROL SYSTEM Johannes Sorteherg, Darien, Conn. (540 Connecticut Ave}, South Norwalk, Conn.) Filed Apr. 7, 1965, Ser. No. 446,154 1 Claim. (Cl. 235-200) The object of my present invention is to devise a novel means for improving the stability measurement of an automatically balanced weighbeam system which I call a Force Bridge used for the purpose of solving the equation AXB=C D where A, B, C, and D represent forces acting upon the weighbeam system.

Reference is made in particular to my prior Patent 2,643,055 in which the above equation has been solved. That system was, however, not entirely satisfactory due to the fact that the original pneumatic Force Bridge is comparatively slow in operation. In order to make a faster device, that is to say, increase the volume of output relative to time, this invention has been developed incorporating a pilot valve for this purpose. I have discovered, however, that when this Force Bridge was used as a square root extractor, it was impossible to achieve a stable output without introducing a restrictive air passage, as hereinafter set forth.

For the purpose of illustrating the invention, I have shown in the accompanying drawings a preferred embodiment of it, which I have found in practice to give satisfactory and reliable results. It is, however, to be understood that the various instrumentalities of which the invention consists can be variously arranged and organized and the invention is not limited, except by the scope of the appended claim, to the exact arrangement and organization of these instrumentalities as herein set forth.

With the foregoing and other objects in view as will hereinafter more clearly appear, my invention comprises a novel weighbeam control system having novel means to increase the stability and reduce the time involved in solving a problem.

FIGURE 1 is a horizontal sectional view of a weighheam system embodying my invention including the pilot valve, shown in balanced position.

FIGURE 2 is an enlarged sectional view of the weighbeam and certain of its adjuncts.

FIGURE 3 is a section on line 33 of FIGURE 2.

FIGURE 4 is a fragmentary section showing the valve in its exhaust position.

FIGURE 5 is a fragmentary section showing the pilot valve in its open to air supply position.

Similar numerals indicate corresponding parts.

Referring to the drawings:

A body portion 1 has an air motor AM, the base 2 of which is mounted on the body portion. The air motor has a rod 3 mounted in it for linear movement and its outer end is connected to a cup 4 having a diaphragm 5 within a housing 6 mounted on the base 2. A spring 7 opposes inward movement of the rod 3.

Fulcrum rollers 8 and 9 are confined in a raceway 10 of a cage 11. The raceway 10 permits the lateral movement of the fulcrum rollers and prevents their longitudinal movement relative to the cage.

Two weighbeams 12 and 13 are suspended from the body portion by leaf springs 14 and 15, respectively, which are laterally adjustable by levers 16 and 17 and screws 18 and 19. The contact lines between the fulcrum rollers 8 and 9 and the weighbeams become the fulcrums F1 and F2. The fulcrum rollers may be positioned anywhere along the weighbeams.

The rod 3 is guided in a bearing 20 in the air motor case 2, and cage 11 is confined between guide plates 21, 22, 23, and 24. The fulcrum rollers 8 and 9 bridge across the guide plates which absorb the difference, if any, between the force A plus B and the opposing forces C plus D produced by load cells A, B,- C, and D which act upon the weighbeams and pairwise on the same center line through thrust rods 25, 26, 27, and 28.

The weighbeams are U shaped in cross section, and are equipped with pins 29, 30, 31, and 32 which absorb the thrust of the rods. The contact lines between the thrust rods and pins become the end fulcrums of the weighbeams.

The weighbeams have extensions 37 and 38 which face nozzle blocks NL and NR with nozzles 39 and 40 and restrictions 41 and 42. The left nozzle 39 is mounted on bellows 43, which in turn is mounted on fixed block 44. The right nozzle 40 is mounted on fixed block 45.

Load cells B, C, and D are assumed to be of the same construction as load cell A, and are of similar construction to those shown in my Patent 3,085,744, but only a load cell connected to a nozzle assembly or the pilot valve must be bellows equipped as shown. The drawings show the connections for a square root extractor. The inputs are to load cells B and/0r D.

The back pressure tap of nozzle block NL communicates with auxiliary bellows 43 and is connected to the air motor AM through passage 46. The back pressure tap of nozzle block NR communicates with the pilot valve through passage 47 and terminates between cap 48 and diaphragm 49. The pilot valve furthermore consists of a main portion 50 with an exhaust port 51 and a second portion 52 with outlets 53 and 54. The outlet 54 is also provided with an output 67. It has further, an inner portion 55 with O-rings 56 and 57, valve seat 58, and a valve disc 59 and spring 60. Completing the assembly are a plunger 61 with exhaust tube 62, return spring 63 and the sealing diaphragm.

Pilot valve parts 61 and 62 are guided by diaphragm 49 and the sliding guide in 55. 61 and 62 move up or down from the balanced mid-position in accordance with the backpressure in passage 47 originated at nozzle 40.

In FIGURE 1, the valve is shown in closed position, as it would appear when the system is in balance. In FIGURE 4 the valve is shown in an exhaust position as it would appear for a decrease in output pressure. FIG- URE 5 shows the valve in its open to air supply position as it would appear for an increase of output pressure.

In normal operation forces represented by A, B, C, and D are exerted on the weighbeams through pressure responsive media such as the bellows. Forces B and/or D may :be transmitted to the weighbeams through other media such as springs, magnets, etc. When the system is in balance, it is evident that the moments of forces A, B, C, and D around fulcrums F1 and F2 present the following equations:

by multiplication we arrive at the equation We are here primarily interested in the square root extracting function wherein A=C, A =BD, or A= /BD.

As stated in the introduction, it is difficult to achieve stable output due to the introduction of the pilot valve which is necessary for high ouput. However, with a suitable restriction 65 in the passage 66 leading to load cell A this difiiculty is completely overcome. Restriction 65 lets air in or out from load cell A at such a slow rate that the air motor is able to keep the left weighbeam continuously balanced without regard to the quick pressure changes from the pilot valve output. Without Patented Dec. 6, 1 966 restriction 65 the fulcrum rollers positioned by the air motor will overshoot and hunting is the result.

Thus, when the system is used for square root extraction, it functions as follows:

From a balanced position, assume there is a change in the input pressure to load cell A, which is also the output from the pilot valve. This will upset the balance on weighbeam 12 with the effect that weighbeam extension 37 will move toward or away from nozzle 39 increasing or decreasing as the case may be, the back pressure in passage 46 to the air motor AM which will try to reposition roller fulcrums F1 and F2 to restore balance. However, the change in the fulcrum roller position upsets the halance on weighbeam 13 with the effect that its extension 38 will move towards or away from nozzle 40, increasing or decreasing, as the case may be, the back pressure in passage 47 leading to the diaphragm chamber of the pilot valve. The pilot valve is shown as a nonbleed type, i.e., when the system is in balance, the exhaust tube 62 will just touch the valve disc 59 in its seated position against seat 58. Increasing the pressure on the main diaphragm 49 beyond what is necessary for the non-bleed or balanced position the valve will open to increase the output pressure, see FIGURE 5, and conversely, decreasing the pressure on the diaphragm will retract the exhaust tube and decrease the output pressure, see FIGURE 4. In each instance both load cells A and C are affected as both are connected to the output of the pilot valve. Due to the high speed pilot valve the fulcrum roller travel would overshoot, creating hunting with resulting unstable output if it were not prevented from doing this by the introduction of restriction 65 inserted in the, passage to load cell A.

The left nozzle is equipped with a small bellows to keep the left weighbeam stationary in relation to the supporting structure. The right nozzle is not equipped with bellows because with introduction of the non-bleed pilot valve the right weighbeam is always in the same position when the system is in balance; in other words: the pilot valve keeps the right weighbeam stationary in relation to the supporting structure.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

An automatically balanced weighbeam control systern comprising two weighbeams, means for transmitting a force to each end fulcrum point of said weighbeams, a movable fulcrum for each weighbeam, latter fulcrums to be in fixed relationship to each other to move in unison along their weighbeams, means for balancing the moments on said weighbeams, a pilot valve with pneumatic output signal, feedback of said output signal to at least two of said force transmitting means, and means for varying the force transmitting means speed of response to said signal.

References Cited by the Examiner UNITED STATES PATENTS 2,643,055 6/1953 Sorteberg 235200 2,991,006 7/1961 Clarke 235----200 3,072,326 1/1962 Rohmann et al 235-200 3,165,262 1/1965 Ollivier 235200 3,190,553 6/ 1965 Sorte'berg 235200 RICHARD B. WILKINSON, Primary Examiner.

LOUIS I. CAPOZI, Examiner.

W. F. BAUER, Assistant Examiner. 

